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Fishery Bulletin 90(3). 1992 



and recreational catch in New York dropped from 840 1 

 in 1982, to 224 1 in 1986, to 10 1 in 1990 (NMFS Cur- 

 rent Fishery Statistics Series). The recreational catch 

 typically represents a sizable fraction of the total land- 

 ings, and at times surpasses the commercial catch (Wilk 

 1979). 



Many weakfish are lost from the fishery as inciden- 

 tal by catch in shrimp trawling operations. The inciden- 

 tal weakfish bycatch, which is greatest in the southern 

 part of the species' range, consists mostly of young- 

 of-the-year fish. It is difficult to determine the magni- 

 tude of the weakfish bycatch, but it is estimated that 

 it exceeds the combined recreational and commercial 

 catch in the southern states (South Carolina, Georgia 

 and Florida) and may approach 30% of the total coastal 

 fishery for adults (Keiser 1976, Mercer 1983, Vaughan 

 et al. 1991). 



The Fishery Management Plan for Weakfish was 

 adopted in 1985 by the Atlantic States Marine Fish- 

 eries Commission (Mercer 1985). At that time, the 

 genetic basis of weakfish stock structure was not well 

 understood, and most states have independently 

 managed their vveakfish fisheries. As a result, different 

 gear restrictions and minimum sizes are enforced along 

 the mid-Atlantic coast. For example, Florida, Georgia, 

 South Carolina, North Carolina, New Jersey, and Con- 

 necticut have no recreational minimum size limit, but 

 a 9-inch size limit is enforced in Virginia, 10 inches in 

 Maryland and Delaware, and 12 inches in New York 

 and Rhode Island. 



A thorough understanding of weakfish stock struc- 

 ture is essential for effective management of the fish- 

 ery. Several management decisions require knowledge 

 of the interdependence of fishery resources from dif- 

 ferent coastal areas. The recent decline in landings 

 from northern waters has coincided with increased 

 catches of large weakfish in the North Carolina winter 

 offshore (sinknet) fishery (Vaughan et al. 1991), but it 

 is not known if the two fisheries operate on the same 

 stock of fish. On a larger geographic scale, the rela- 

 tionship between bycatch mortality of young weakfish 

 in southern waters and landings of older weakfish in 

 northern waters in subsequent years has not been 

 determined. A detailed genetic analysis of weakfish 

 stock structure would provide information required to 

 test hypotheses of the independence of weakfish from 

 different coastal areas. 



Several studies have investigated weakfish stock 

 structure employing a variety of ecological and mor- 

 phological techniques including mark and recapture 

 data (Nesbit 1954), scale circuli patterns (Perlmutter 

 et al. 1956), morphological characters (Seguin 1960, 

 Scoles 1990), and relative growth rates and reproduc- 

 tive characters (Shepherd and Grimes 1983, 1984). 

 Most of these studies concluded that weakfish comprise 



two or more stocks; however, the inability to distin- 

 guish between ecophenotypic and genetic character 

 variation in these studies has confounded interpreta- 

 tion of the results. 



There are few studies on the biochemical genetics of 

 the weakfish. Crawford et al. (1989) analyzed water- 

 soluble protein variation using starch gel electro- 

 phoresis. They found no significant genetic differen- 

 tiation between weakfish collected from Buzzards Bay 

 MA to Cape Hatteras NC, and so were unable to 

 disprove the null hypothesis that weakfish along the 

 mid- Atlantic coast share a common gene pool. Of the 

 25 protein-encoding loci surveyed in the Crawford et 

 al. (1989) study, only two were polymorphic within the 

 pooled sample, and the mean heterozygosity was low 

 relative to other marine fishes. 



Studies of protein variation have been extremely 

 useful in demonstrating the intraspecific genetic struc- 

 ture of many marine fishes (reviewed in Ryman and 

 Utter 1987). For those species which display little in- 

 traspecific variation, like the weakfish, sample sizes 

 must be very large to detect significant differentiation 

 between putative stocks, if it exists. In such cases, 

 analysis of a more rapidly evolving set of molecular 

 characters may provide a better estimate of population 

 structure with a more manageable number of samples. 

 Restriction fragment length polymorphism (RFLP) 

 analysis of mitochondrial DNA (mtDNA) has provided 

 such a tool, and the technique has been useful in resolv- 

 ing stock structure within species which exhibit little 

 protein variation (reviewed by Ovenden 1990). 



This paper reports the results of an RFLP analysis 

 of weakfish mtDNA to determine if fish along the mid- 

 Atlantic coast share a common gene pool. The study 

 began as a spatial and temporal investigation of a large 

 number of individuals from a few collection sites along 

 the central mid-Atlantic coast with 6 restriction endo- 

 nucleases. Because there was a high degree of genetic 

 homogeneity among these samples, we expanded the 

 investigation to include an intensive analysis of weak- 

 fish from the northern and southern ends of the species' 

 range with 13 restriction endonucleases. 



Materials and methods 



For our sampling protocol we assumed that if separate 

 genetic stocks of weakfish exist, they should be separ- 

 ated at the time of spawning. We therefore restricted 

 our collections to female weakfish that were ready to 

 spawn as evidenced by high gonadosomatic indices 

 (GSI). For example, the mean GSI of the New York 

 1988 sample was 7.7% + 3.1 SD. 



Ripe, female weakfish were obtained from commer- 

 cial fishermen, sportfishing tournaments, and the 



